Influence of roughness on the early corrosion of API steels by atomic force microscopy (AFM): A real-time assessment

Roughness surface significantly affects the corrosion process of steels. However, this relationship in early stages at the local level has not been well studied. The mechanisms associated with the beginning of corrosion are thus not well known. Likewise, the lateral distribution of roughness is rarely considered, which can lead to inaccurate representations of surface features. Herein, the effect of roughness on the deterioration of carbon steels was locally studied by means of a fluid cell (FC) coupled to an atomic force microscope (AFM). The steel studied was prepared using grit papers with different abrasive particle sizes (#600, #1500, #2000) and exposed to artificial seawater for 4 h. A power spectral density (PSD) approach, which considered lateral distribution of surface roughness, was used to compare with traditional statistical roughness parameters. According to the roughness evolution, the corrosion susceptibility was #600 > #1500 > #2000, indicating greater corrosion resistance for smoother surfaces. The calculus carried out for estimating the corrosion rate as function roughness variation dictates that there may be up to three stages in the onset of corrosion. The first and third stages show a low corrosion rate (considerably less than 4 ×10−6 A/cm2), while the middle stage reflects an accelerated corrosion rate (up to 5.3 ×10−5 A/cm2 for #600 at 2 h). These results were in concordance with conventional electrochemical impedance spectroscopy tests. This method is proposed as a preventive strategy for the assessment of pipeline materials integrity which are used for transporting petroleum industry products.